Magnetic keyboard



Dec. 10, 1957 M. CANEPA MAGNETIC KEYBOARD Filed Jan. 14, 1955 lrm w v vaw k. m MW Z Wu United States Patent Ofiice 2,816,254 MAGNETIC KEYBOARDMichele Canepa, South Norwalk, Conn., assignor to Olivetti Corporationof America, New York, N. Y., a corporation of Massachusetts ApplicationJanuary 14, 1955, Serial No. 481,735 7 Claims. (Cl. 317--158) Thisinvention relates to keyboard mechanisms and particularly to a magnetickeyboard which provides the type of action wherein one or more keys arereleased only after one or more other keys are depressed.

Although innumerable keyboard mechanisms of one kind or another havebeen devised in the past for use in typewriting machines, calculatingmachines, tabulating machines, and the like, none of these, so far as Iam aware, operates as simply and yet effectively as the keyboard which Ihave invented. Briefly, according to the invention, I provide aplurality of key actuated members of magnetically permeable material,each being adapted to be moved from one position to another when the keyassociated therewith is depressed. Tending to maintain each key actuatedmember in the actuated position, by magnetic attraction, is aflux-limiting flux generator magnetically connected thereto, theactuated member forming, when in its said actuated position, a part of acomplete low reluctance magnetic circuit including the flux generator;while tending to return each key actuated member to its originalposition, thereby disestablishing the magnetic circuit formed with theflux generator to release the key, is a biasing device, such as aspring. The individual springs, however, are not so strong as toovercome the magnetic holding force on a single key actuated member, oron any predetermined number of these members less than all of them, whenplaced in circuit with the flux generator. Rather, it is only whenadditional keys are depressed, and the magnetic flux produced by theflux generator, which is limited as aforesaid, is distributed among morethan the predetermined number of key actuated members that the springswill be able to overcome the magnetic holding force.

Accordingly, in one embodiment of the invention with only one keydepressed, a single series flux path, including the flux generator andthe one key actuated member, is formed, providing suflicient magneticforce to maintain the key actuated member in position. When a second keyis depressed, however, a second flux path, in parallel with the firstpath, is created, diverting roughly half of the flux from the first keyactuated member to the second. As a result, the magnetic holding forceon the first key actuated member will be materially decreased,permitting the biasing spring to return it to its original positionthereby releasing the key associated therewith. Since there remains onlya single flux path through the second key actuated member, substantiallyall the flux in the saturable member passes therethrough providing aholding force greater than the force of the spring as was the caseinitially with the first key actuated member. Only after another key isdepressed will the second key actuated member be released, and so forth.

It will be understood, of course, that the key actuated members may beconnected in operative relation to appropriate elements (not shown) ofadding machines, computers, electric typewriters, or other businessmachines, etc. Indeed the novel device of the invention is usefulwherever a keyboard may be employed and it is 2 desired that thedepression of succeeding keys should re lease previously depressed keys.

It is an object of this invention, therefore, to provide a keyboardbased on magnetic principles to the end that a greatly simplifiedstructure is afforded. The novel features of this invention, togetherwith further objects and advantages thereof, will become more readilyapparent when considered in connection with the accompanying drawingwherein:

'Fig. 1 is a view in elevation of a keyboard according to my inventionemploying an electromagnetic flux generator; and

Fig. 2 is a fragmentary view of a single key assembly and flux generatorsimilar to that in Fig. 1, but employing a permanent bar magnet as thesource of flux.

Referring now more specifically to Fig. l of the drawing, wherein likeelements are designated by the same reference characters, it will beobserved that in the par ticular embodiments shown the keyboard of myinvention comprises, in the main, three flux-limiting flux generators11, a plurality of key assemblies 12, including magnetically permeablekey actuated members 13 adapted to be coupled to the flux generators 11by means of coupling members or pole pieces 14a and 1412. Each of theflux generators 11 is made up of a magnetically saturable member 15surrounded by a magnetizing winding or coil 16 to produce, whenenergized,'an amount of flux in the saturable member sufiicient to causesaturation. Coupling members 14a and 14b magnetically intercouple thesaturable members 15 to which they are joined, and, in addition, serveto guide the flux in the saturable members through key actuated membersor rods 13 when the latter are appropriately positioned. To this end,the coupling member 14a is apertured, as at 20, to receive the variouskey'actuated members or rods 13 for axially slidable movement between areleased position and a depressed position wherein they engage the othercoupling member 14!) forming parallel magnetic circuits with fluxgenerators 11. Each key assembly 12 includes besides the rod 13, a keytab 19 and a biasing spring 18 between tab 19 and the apertured couplingmember 14a. A stop ring 17 on each rod 13 limits its upward travelwhereas engagement of the lower face of rod 13 with the lower couplingmember 14b limits its downward travel.

in operation, when one of the key actuated members or rods 13 isdepressed, so that it engages the lower coupling member 14b (as the nextfrom the left rod shown in Fig. 1), there is provided for each of theflux generators 11, a low reluctance path entirely through magneticallypermeable members, namely members 14a, 14b, 15 and the depressed member13. As a result, members 15 become saturated, since their permeabilitiesand cross-sectional dimensions relative to the number of turns on thecoils 16 and the amounts of current passed theretrough are chosen toinsure that saturation takes place. On the other hand, thepermeabilities and cross-sectional dimensions of coupling members 14aand 14b, and key actuated members 13 are such that they do not becomesaturated. In fact, it is most desirable to make coupling members 14aand 14b quite large in cross section to minimize their reluctance sothat the amount of flux present in a particular depressed key actuatedmember will be substantially independent of its position with respect toflux generators 11. Due to the presence of the flux in the depressedmember 13, there is created a magnetic holding force tending to maintainmember 13 in engagement with coupling member 14b, and by properlydesigning the various magnetically permeable members in accordance withwell known magnetic principles, this magnetic force can be made justlarge enough to prevent its being overcome by spring 18. If however, asecond key actuated member 13 is depressed, a second low re- PatentedDec. 10, 1957 luctance path will be created for the flux in saturablemembers 15, and since substantially no more flux can emanate frommembers 15, as they are saturated, a portion of the flux that was in thefirst key actuated member to be depressed, roughly half, is divertedtherefrom to the second key actuated member. In this Way, the fluxdensity in the first key actuated member is materially reduced, as isthe corresponding magnetic attraction or holding force, so that now theforce exerted on the first key actuated member by spring 18 issufficient to disengage it from coupling member 14b, and to return it toa released position wherein the magnetic circuit therethrough iseffectively broken by the creation of a substantial air gap. All of theflux in the saturable members '15 will now flow in the second keyactuated member to be depressed, thereby providing a holding forcesufiicient to maintain it in a depressed position, as was initially thefirst key actuated member. As each succeeding key is depressed, the sameoperations will of course take place.

In Fig. 2 I have illustrated the invention substituting a permanent barmagnet 11a for the saturable core and magnetizing winding of fluxgenerator 11 of the previous embodiment. The bar magnet 11a is so chosenwith respect to size and strength as to be substantially incapable ofdelivering more flux than is present when only one of the members 13 isdepressed and therefore only one magnetic circuit between the poles ofthe magnet is established. Hence, the depression of an additional member13, doubling the permeance of the path from pole to pole of the magnet11a, does not cause any appreciablc increase in the total flux generatedby the mag net but rather serves to redistribute the flux between thedepressed members 13 with the result that the first member 13 will bereleased by the action of its biasing spring and the second additionaldepressed member 13 will then be magnetically held. Thus, the operationof the embodiment of Fig. 2 is the same as that of Fig. 1, justdescribed.

Although only a single row of keys has been illustrated by way ofexample, it will be apparent that any number of rows may be providedaccording to my invention as the use to which the keyboard is put maywarrant. Also, depending on the number of keys to be accommodated, asfew as one flux generator or more than three flux generators may beutilized. Various other modifications, particularly modifications of thesimplified structural embodiment of my invention illustrated, will occurto those skilled in the art, and therefore, it should be understood thatI do not wish to limit my invention to the precise embodimentillustrated. Rather the invention should be deemed to be limited only bythe scope of the appended claims.

What is claimedis:

1.. A magnetic keyboard comprising a flux limiting flux generator, aplurality of key actuated members of magnetically permeable material,each being adapted for movement between .a first position to establish aclosed magnetic circuit including said flux generator .and a secondposition to disestablish .said circuit, and biasing means tending tomove said key actuated members out of said first position, the maximumamount of flux said flux generator is capable of delivering being sorelated to the reluctance .of said key actuated members and the force.of said biasing means that the magnetic vholdingforce caused by themagnetic flux in said key actuated members is sulficieut to maintainonly a predetermined number of them in said first positionsimultaneously.

2. A magnetic keyboard comprising a flux limiting source of flux, aplurality of key actuated members of magnetically permeable materialmovably mounted in operative relation to said source, each of said keyactuated 'members being movable between a first position wherein a-lowreluctance path including said source and the key actuated member isestablished, the flux in the key actuated member tending to maintain itin said first position, and a second position wherein the reluctance ofsaid path is greatly increased by the presence of an air gap, andbiasing means urging each of said key actuated members out of said firstposition, the magnetic characteristics of said members and the maximumflux characteristic of said source being so chosen with respect to thestrength of said biasing means that only a predetermined number of saidkey actuated members will be held in said firsttposition simultaneously.

3. A magnetic keyboard comprising a flux limiting flux generator, polepieces individually coupled to the poles of said flux generator, aplurality of key actuated members of magnetically permeable materialmovably mounted in operative relation to said flux generator, each ofsaid key actuated members being movable between a first position whereit is in contact with said pole pieces and a second position Where it isout of contact with at least one of said polepieces; and biasing meansurging each of said key actuated members out of said first position, themaximum amount of flux said generator is capable of delivering being sorelated to the magnetic characteristics of said membersand the strengthof said biasing means that only a predetermined number of said memberswill be held in said .first position simultaneously by the magnetic fluxtherein.

4. A magnetic keyboard according to claim 3 wherein said key actuatedmembers are in slidable engagement with the other one of said polepieces.

5. A magnetic keyboard according to claim 4 wherein said key actuatedtmembers consist of rods, said other of the pole ,pieces being.apertured to receive said rods.

6. A magnetic keyboard comprising a magneticallysaturable.memben'magnetomotive means associated therewith to generate anamount of flux therein sutficient to cause saturation thereof, polepieces individually coupled to thepoles of said saturable member, aplurality of key actuated members of magnetically permeable materialmovably mounted in operative relation to said saturable member, each ofsaid .key actuated members being movable between a first position whereit is in contact with said pole pieces and a second position where it isout of contact with at least one of said pole pieces, and biasing meansurging each of said key actuated members out of said first position, themagnetic characteristics of said members and the strength of saidmagnetomotive force being so chosen with respect to the strength of saidbiasing means that only a predetermined number of said key actuatedmembers will be maintained in said first position simultaneously by themagnetic flux therein.

7. A magnetic keyboard comprising a permanent magnet, pole piecesindividually coupled to the poles of said magnet, a plurality of keyactuated members of magnetically permeable material movably mounted inoperative relation .to said magnet, each of said key actuated membersbeing movable between a first position where it is in contact-with saidpole pieces and a second position where it is out of contact with atleast one of said pole pieces, and biasing means urging each of said keyactuated members out of said first position, the magneticcharacteristics of said members and the strength of said magnet being sochosen with respect to the strength of said biasing means that only apredetermined number of said elements will be maintained in said firstposition simultaneously by the magnetic flux therein.

References Cited in the file of this patent UNIT ED STATES PATENTS

